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Tuning into sunlight using DNA

Our farm gets its power from traditional silicon solar panels. But I have long been interested in the idea of using tiny antennas that resonate at light frequencies to collect solar power using what are called rectennas. A rectenna is an antenna connected to a diode that “rectifies” alternating current into direct current.

Making antennas half the size of a wavelength of light is a nanotechnology challenge, but several designs have been fabricated and tested in laboratories. The main reason for the excitement is that such a system can, in theory, reach efficiencies of 85%, compared to silicon efficiencies below 30%.

One of the main problems in nanotechnology is building those tiny things. Especially in the huge numbers needed to coat a big solar panel. But new techniques in making tiny shapes out of DNA may come to the rescue. Paul Rothemund has been making things out of DNA for years, working on building computers out of DNA to solve difficult problems in computation.

Researchers have already made DNA conductive like a metal, and made metallic arrays using DNA scaffolding. They have used ink-jet printers to paint surfaces with DNA. It seems to me that building tiny antennas and the low pass filters and MIM diodes needed for an optical rectenna is possible using DNA to form the parts, and coat them in regular arrays over large surfaces.

The DNA would self-assemble the antennas into large thin-film crystals to convert sunlight into electricity.

Categories: Chemistry, Environment, Genetics, Physics.

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Precious metal

I am not a commodoties trader, but I buy the metal indium in large quantities, and process it into liquid metal alloys and alloys that melt in hot water.

I used to buy indium for about $50 per pound. Now it costs ten times that.

Indium is about three times more abundant in the earth’s crust than silver or mercury, although some sources claim it is about the same as silver. So why has the cost of indium gone from much less than silver to much more than silver?

Big screen televisions.

Big screen displays need to have an electrically conductive coating on the glass that is transparent. Tin oxide can be used, but it is not as conductive as indium tin oxide. That 60 inch big screen TV is coated in indium tin oxide. So is the display in your laptop computer, your cell phone, and your personal digital assistant. And indium tin oxide is 90% indium oxide, and only 10% tin oxide.

Indium is also used in several semiconductors, in welding, and in nuclear control rods. But none of those industies has grown as fast as the number of flat screen displays, or the number of square miles of flat screen display produced since this century began.

And I do my part. The demand for a non-toxic liquid metal to substitute for mercury is surprisingly high, and I sell a lot of it these days. And since I buy indium in bulk, my customers get last year’s price, until I run out. Then I will have to swallow hard and write a big check for the next batch.

Categories: Chemistry, Physics.

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Small scale Jurassic Park

An email from a friend caused a chain of events that led me to a wonderful paper by Charles Kerfoot, about resurrecting fossil eggs from progressively deeper and older layers of sediment in a lake, and hatching the eggs from different layers to compare the creatures (Daphnia retrocurva) as they evolve over time.

As these eggs are covered in sediment, they remain dormant (in facultative diapause) for as long as 300 years or more (the paper only shows data going back to 1825).

In lakes that freeze over, sediments arrange in annual layers called varves. They can be counted like tree rings. In addition to counting the annual layers, the sediments were also dated by Cesium, Potassium, Radium, and Lead radio-dating, which confirmed the dates done by counting.

The eggs from different layers were hatched, and the Daphnia (water fleas) that grew from them show differences in the body armor over time as they adapted to evolving predators. Genetic analysis also shows evolution, both in mitochondrial DNA, and in allozyme analysis, where enzymes that differ only in their amino acid sequence show where specific mutations in a gene have ocurred.

By tracking the mutations as they accumulate in successive generations, further confirmation of the date sequences and evolutionary change becomes visible.

Other eggs and fossil remains show how the predators of Daphnia evolve to keep up with defensive adaptations by their prey.

By hatching dormant eggs from sediments laid down over hundreds of years, we can watch evolution progress right in front of our eyes, in a complex crustacean, not just in bacteria and viruses.

Categories: Biology, Environment.

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Long Distance WiFi

I live on a mountain.

I get my high speed Internet by using a microwave link from a tower on the hill near the house to the top of a tall building in San Jose, a distance of about 11 miles.

Since that link provides me with much more bandwidth than I actually use, even when streaming video from my henhouse, I give free Internet access to those of my neighbors who don’t have line-of-sight to San Jose. Some of the links are what we call “wires through the woods”, but several are WiFi links, using directional antennas and Linksys WRT54G wireless routers.

Our longest link is 2.89 miles, to a house across a canyon from me, on another ridge to the east. But just for fun, I set up a dish aiming at distant Fremont, and put another dish on the lumber rack of my pickup truck and drove to a hill above that city and parked on the side of the road, aimed my dish towards home, and got a solid signal at a distance of a little over 26 miles as the crow flies. I was getting a nominal 5.5 megabits per second at that distance, which allowed me to get actual measured throughput of just under 3 megabits per second. Surfing the web was still plenty fast enough, and what delay I was seeing was the normal server delay. I could not really tell any difference, subjectively, from surfing at home.

I would have gone farther, but I had run out of road.

Back home, I drove to the top of the mountain, and aimed my dish around at various parts of Silicon Valley and beyond, and used the NetStumbler program to find access points. At one point, I was able to get a signal from a transmitter in Oakland, about 45 miles away.

I was feeling pretty proud of myself, with my truck mounted 24 dBi microwave dish and my 300 milliwatt WiFi card in the laptop computer.

Then I read about some guys who went just under 125 miles using 300 milliwatt cards in their laptops, feeding 10 and 12 foot parabolic dishes — one towed on a trailer.

As I had found in my own experiments, the hard part is finding two places within line-of-sight of one another that are far enough away to make the project interesting. These guys set up one dish on a mountain in Nevada, and then drove into Utah.

To get farther than mountaintop to mountaintop, some Swedish folks put a WiFi unit in a balloon and sent it up to an altitude of over 18 miles, and received signals from it as far away as 195 miles away. They used a 6 watt amplifier, since a 12 foot parabolic dish is a little heavy for a weather balloon to lift, and somewhat hard to aim.

Years ago I used my amateur radio equipment to talk to astronauts in the Space Shuttle and International Space Station. There are amateur satellites in orbit that store and forward email to amateurs around the world. WiFi and satellites are already connected to provide Internet access to recreational vehicles. It seems to me it is only a matter of time before a low earth orbiting WiFi access point breaks all earthly records for distance.

Categories: Computers.

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Can you see the Milky Way?

The National Park Service estimates that two-thirds of Americans can’t see the Milky Way from their backyard because of light pollution. And 99% of the population lives in areas considered light polluted.

At the rate light pollution is increasing, by 2025 there will be no areas in the continental U.S. that are not affected.

Most of the light pollution is caused by wasting electricity. Street lights that aim their light up into the sky are wasting the energy used to make the light. By properly aiming it down where it is needed, money and energy are saved, and people can see the stars again.

Like other forms of pollution, bright city lights are causing harm to wildlife, such as migrating birds, sea turtles, and nocturnal animals such as California’s glossy snake. When darkness never falls, predators that hunt in twilight can hunt all night, and the adaptations nocturnal animals depend on are no longer effective. Nocturnal salamanders wait for dark to hunt, and get less food in brightly lit areas. Light affects hormones that tell frogs when to put on fat for egg laying, and fireflies don’t mate near incandescent lighting.

Astronomers have been complaining for a long time about light pollution.

We can fix light pollution and save money by doing it. People just need to pay attention to where the light is going. Aim low.

Categories: Astronomy, Environment.

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By Simon Quellen Field
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